Simplify LimitTests
Simplify LimitTests

Limit tests currently used for SQL backend testing are too complex.
Due to this complexity they could be used for SQL only. They assumed
possibility to create a domain, while it is not possible when LDAP
identity backend is used with multidomain support.

Simplify LimitTests and assume that a default domain is used for all
operations.

Change-Id: I77d581e03dae86c299ce2e1e56164dde3c4ad72a

ilay09/keystone,klmitch/keystone,ilay09/keystone,mahak/keystone,openstack/keystone,dims/keystone,klmitch/keystone,dims/keystone,ilay09/keystone,rajalokan/keystone,cernops/keystone,mahak/keystone,rajalokan/keystone,himanshu-setia/keystone,mahak/keystone,cernops/keystone,openstack/keystone,openstack/keystone,himanshu-setia/keystone,rajalokan/keystone